I am using GMF diagram only to view. The XMI file containing the information of nodes and edges is
generated by another program. As I have in my current example 10,000 nodes and about 15,000 edges to
open the diagram takes quite a while.
I already removed the labels of the edges but the time did reduce only 15% and takes still a long time.

I found the time spend to open the diagram updates all the AncestorHelpers. I imagine these are used
for editing only.

Is there a way to remove the edit functionality? I do not need to draw new edges or to add nodes but
I still want to bend existing edges.

I don't know which part you can remove or not. i think that you should try and you will see

Otherwise, an idea to improve performance will be to use a binary serialization. This is something done in EMF but not yet in GMF. But if it is really important, I think that it will be a good way to improve the overall performance.